The present invention relates to a loop-type optical dataway system.
A conventional loop-type optical dataway system has a double loop configuration as shown in FIG. 1.
Data transmission stations 13.sub.1, 13.sub.2, . . . , 13.sub.N are connected in optical fiber cables 11 and 12 to form the double loops. Each station 13.sub.i (i=1 through N) has optical receivers 21 and 22 for performing photoelectric conversion of light signals received from the optical fiber cables 11 and 12, and optical transmitters 31 and 32 for performing electrical/optical conversion of the input signals from the optical receivers 21 and 22 and producing the output light signals supplied to a following circuit through the optical fiber cables 11 and 12.
Data transmission is generally performed through one of the optical fiber cables 11 and 12. Assume that data transmission is being performed through the optical fiber cable 11. Then, a light signal supplied to the station 13.sub.i through the optical fiber cable 11 is converted into an electrical signal by the optical receiver 21. A converted output signal from the optical receiver 21 is supplied to a station controller (not shown) and to the optical transmitter 31. The optical transmitter 31 also receives an intra-office send signal from the station controller. The optical transmitter 31 converts the input signal into a light signal. The output light signal from the optical transmitter 31 is supplied to a following circuit through the optical fiber cable 11.
When a fault occurs in the optical fiber cables 11 and 12 or in the station 13i, the optical fiber cables 11 and 12 are connected before and after the fault section so as to form U-links (return links). Data transmission can be performed through the line excluding the fault section. FIG. 2 shows a system configuration after system reconfiguration when a fault occurs at the station 13.sub.1. In FIG. 2, U-links are formed at the stations 13.sub.N and 13.sub.2 before and after the station 13.sub.1. Thus, the fault station 13.sub.1 is isolated from the system, and data transmission between the stations 13.sub.2 through 13.sub.N can be performed through the optical fiber cables 11 and 12 (double loops).
In a double loop system as described above, U-links are formed to reconfigurate the system, thus allowing data transmission between stations after a fault occurs.
However, system reconfiguration in the prior art can only be performed when the fault occurs in a single station or in a single portion of the cables. Therefore, when two non-consecutive stations, for example, stations 13.sub.1 and 13.sub.4 are turned off for maintenance or modification, data transmission cannot be performed between the stations 13.sub.2 and 13.sub.3 and stations 13.sub.5 through 13.sub.N.